Railway signaling systems



March 21, 1961 c. w. FAILOR ET Al. 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 1 Filed Oct. 28, 1957 u A 8 B E m 5 HE G M M M 3 Bums RQQNN kwmmx u A m lzavles W 1226222! and BY Gran/End l3 5229M?! March 21, 1961 c, w FAILOR ET AL 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 2 1 Fang Filed Oct. 28, 1957 March 21, 1961 c. w. FAlLOR ET AL 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 5 Filed Oct. 28, 1957 INVENTORS Charles- W FQLZOP and BY auwiald z. s zes.

6d A uzlfi I'Wlll ATTORNEY 8i w n n T N w m fi u K Q kmm m E wsuw ww fiakmmw N% 1 fxu RQRN March 21, 1961 C. W. FAILOR ET AL 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 4 Filed Oct. 28, 1957 March 21, 1961 c, w FAILOR ET 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 5 Filed Oct. 28, 1957 March 21, 1961 c. w. FAILOR ET AL 2,976,404

RAILWAY SIGNALING SYSTEMS 6 Sheets-Sheet 6 Filed Oct. 28, 1957 CPawfa d E. B!

M NN WY hm QM QM M bw .Q-+ N 6% l ll M WW+ M UN+ Wu? bw? Wm? g \wwwwmwwww my E Mn olllll. A ll .luxlllllllllll': l l Ill'lllllllllllllli Ollllllllllli'lllll THEY/i HTTOH/VFY Patented Mar. 21, 1961' RAILWAY SIGNALING SYSTEMS Charles W. Failor, Forest Hills, and Crawford E. Staples, Homewood, Pa., assignors to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvama Filed on. 28, 1957, Ser. No. 692,926

4 Claims. (ca. ZINE-33) controls movement of traflic in both directions over a stretch of single track railway. Particularly, our invention relates to an A.P.B. system incorporating coded track Circuits to eliminate the use of line wires for control purposes.

Economy in installation, apparatus, and maintenance is desirable in any railway signaling system provided that this economy may be obtained without the sacrifice of any safety features or characteristics. The major expense in many A.P.B. systems has been the line wire necessary for control circuits and the maintenance of these line circuits. Thus coded track circuits, as known today, provide an advantage by requiring no line wires, especially when such coded track circuits utilize both master (normal) and feedback (reverse) codes. In the past, the power requirements of such a coded track system have sometimes been considered excessive, especially where commercial power is not readily, available. This heavy power requirement is due principally to the-wellknown electrical resonance type decoding circuits. However, the development and use of relays of the code following type with mechanically tuned, frequency responsive contacts eliminates much of this'heavy power drain. Such relays may be of the general type disclosed and claimed in Letters Patent of the United States 2,730,592, granted in January 10, 1956, to Andrew Hufnagel for a Code Following Relay With Frequency Decoding Confacts. In addition to these relays,the reduction in the 7' amount of apparatus used presents another means of economizing in such signal systems. V

With the utilization of longer track circuits and the type-of control for directional stick relays is frequently termed advance pickup. This feature provides overrunp'rot'ection-at the signals, hand-throw switch pro.- tection, andthe' display of the most restrict1ve,11.e., stop,

indication by each opposing signal immediatelybehind a train. This particular safety factor is easilyprovided in linewire signal systems, but has not always been provided in codedtrack systems. v 1

It is,"ther'etore, an object of our invention to provide a coded track A.P.B. signal system for single track railways using no'line wires. f

Another object of our invention is to providea continuously energized, coded track A.P.B. signal system using master and feedback codes. Y

'A further object of our invention coded track A.P.B. signal system using mechanically tuned, frequency responsive decodingapparatus.

is to provide a elimination of line wirecontrolfor A.P.B. signal sys- Another object of our invention is to provide anim-' 7 proved coded track A.P.B. system using less apparatus and with greatly reduced power requirements.-

It is also an object of our invention to provide,

such a signal system, the feature of advance pickup of the directional stick relays.

Still another object of our invention is to provide a coded track, non-line wire A.P.B. signal system which embodies all the safety features or characteristics usually associated with similar signal systems using line wire control circuits.

Other objects and features of our invention will become apparent as the specification proceeds when taken in connection with the accompanying drawings.

Referring to the drawings,

Figs. 1A to 1B, inclusive, when placed adjacent in order from left to right with Fig. 1A at the left, show diagrammatically one form of apparatus embodying our invention, as used in the A.P.B. signal system for a particular stretch of single track.

Fig. 2 of the drawings provides a signal control limit diagram for the single track stretch and also includes indications of the coded energy normally in the track circuits.

Similar reference characters refer to similar parts of the apparatus in each of the drawings.

In practicing our invention, signal controls are transmitted over the rails of the single track stretch by the use of coded track circuits. A neutral master (normal) frequency code is used to control the wayside signals generally in one direction and polar feedback (reverse) code is used to control the wayside signals generally in the opposite direction. However, some variation in the direction of flow of the track codes is necessary between the various track sections formed in the single track stretch between adjacent stations. Within any one particular track section, the master code always flows in one direction and the reverse code in the opposite direction. The signal controls transmitted through these coded track circuits are obtained by mechanically tuned frequency responsive decoding of the master or frequency code using,

as an example, the code following relay disclosed in the V previously rnentionedHufnagel patent. Non-tuned relay energized due to the occupancy of the adjacenttrack sections as a train passes the signal in thedirection for which that relay is'designated. This advance pickup of the'dire'ctional stick relays is obtained either by the use I 'of two series approach relays, one in each "adjacent track circuit, or by the combination of a singleseries approach'relay in one circuit and-the code detecting relay l I a for the frequency track code in the other circuit.

directional stick relay circuits provide'ope'ration and protection identical with that provided by any of thewell known systems using non-coded track circuits andline; 3

wire control circuits. In other words, the present invenltion provides equivalent operation and'protectionwhen' I: hand switches are thrown or it signals are overrun and f assures that each opposing signal displays'its most' restrictive aspect immediately behind each trainfmove'y men-t.

Referring now to i 7 when placed adjacent 'in order from leftto iright wi th Fig, 1A atthe left, an A.P.B. signal system is shown" I for a stretchiof single track railway extending; between stations X and Z. In the remainder of this descriptiomflg Figs. 1A to lEof the drawings? the direction from X to Z will be considered the eastbound direction. It is to be noted that the same stretch of single track plus some extension at both.ends is also shown in Fig. 2 which will be discussed in greater detail hereinafter. At each of the stations X and Z, there is provided a passing siding for the purpose of making meets between opposing trains or passes by trains in the same direction. The eastern end of the passing track at station X is connected to the main track over switch 11W while the western end of the similar siding at station Z is connected to the main track over switch 5W.

In each of the drawings, the single track as well as the passing tracks are shown by the conventional single line symbol. This stretch of track is divided into track sections which are separated electrically from each other by the usual insulated joints which are shown as short heavy lines at right angles to the track symbol. Each of these track sections is designated by the reference character T with a prefix in accordance with the signals at each end of the section. Where possible, the numerical prefix is in accordance with the opposing signals governing movements in opposite directions into the particular track section in question. It will be noted that each insulated joint as shown in the parts of Fig. l is either a double or a single signal location. it is to be understood that other insulated joints may be used to provide what areknown as cut sections for the purpose of repeating the track circuit energy. However,

such cut sections are not shown in this application as they are not necessary for an understanding or a showing of the circuits of our.invention.

Each of the signals is indicated bythe reference character G with a numerical prefix ascending in order from the eastern end to the western end of the. stretch. As shown, signals 66, SG, 166, and 12G control eastbound traflic while signals 5G, 7G, 9G, and 11G control westbound trafiic in the single track stretch. Signals 5G and 126 are further termed as station-leaving or headblock signals while signals 66. and 1 16 are likewise known as home or station-entering signals. All other signals shown in any part of Fig. 1 are intermediate signals.. The signals may be of any well known type but are here shown for simplicity as the color-light type. Each signal is'thus provided with three lamps, green,

' yellow, and red, referenced respectively as G, Y and R. In each signal, a single lamp will be lighted to provide a signal aspect, the indications resulting from: the green, yellow, and red aspects being, respectively, clear, approach, and stop. The track locations of these signals are indicated adjacent the track symbol by conventional three position semaphore symbols, each trackside symbol being connected by a dotted line to the corresponding lamp group where the signal control circuits are shown. It is to he further noted that, in the'semaphore symbol shown adjacent the track symbol, the normal aspect displayed by each signal is indicated by a heavy line in the corresponding position.

Each signal location is supplied with a local source of direct current energy which may be a battery of the proper size and capacity. For simplicity, such energy sources are not shown in the drawings, but only the positive and negative terminals thereof are indicated by the references B and N, respectively.

Certain relays used in the system are of the slowrelease type, this characteristic being provided by the relay construction and/ or by snubbing circuits connected in multiple with the relay winding. The contacts of such relays are designated as being slow release by downward pointing arrows drawn vertically through the movable portion of each relay contact. Other relays in the system are of the biased type and are so indicated by a horizontal arrow within the symbol for the relay winding. Track relay IZTR (Fig. 1A) is an example of a biased relay. Such relays are so designed that they Wlll be energized properly to close front contacts only when the flow of current in the relay winding is in the direction of the previously mentioned arrow. Current flow in the opposite direction or deenergizing the relay results in the closing of back contacts of the relay. The contacts of such biased relays are shown in the conven tional horizontal plane.

Some of the biased relays, such as track relay 11TR (Fig. 1A), are provided with two separate and distinct armature structures, termed for convenience the normal and reverse armatures. Each armature is provided with an associated set of contacts whose operation is separate from that of the other set of contacts. Each armature is responsive to current flowing through the relay winding in one direction only, operating to close associated front contacts only under this condition. At all other times, the armatures are biased to close associated back contacts, as in any biased relay. The normal armature of relay llTR, for example, is responsive only to current flowing through the winding in the direction of the lefthand arrow, designated :1, within the relay symbol. The reverse armature is responsive only to current flow of the opposite direction, indicated by the second arrow within the relay symbol designated r. The contacts associated with the normal armature are designated by a sufiix )2 added to the conventional letter references for the contacts. Each contact associated with the reverse armature is identified by the sufiix r added to the otherwise conventional letter reference for the contact. Each double armature biased relay in-the circuit arrangement is shown and referenced in a similar manner. As contacts of these relays are referred to throughout the description, the use of the suffixes n and r will serve to distinguish between the two sets of contacts. It is to be understood, (however, that any of these double armature, biased relays may be replaced by two ordinary biased relays having a single armature each. If used, the windings of the two relays are connected in series so poled that one relay is responsive to current flowing in one direction through the series circuit while the second relay is responsive to current flowing in the opposite direction.

Relays which are used for transmission of the master code into the track rails are of the magneticstick type, as represented by relay llCTP shown in Fig. 1A. The contacts of such relays are shown in the vertical plane and the relays are indicated by an arrow in the winding symbol the arrow denoting the direction of current flow which will result in the closing of normal or left-hand contacts. Current flow in the opposite direction results in the closing of right-hand or reverse contacts. Such relays maintain their contacts in the position to which they were last operated when the relay winding becomes deenergized.

Each signal location, except signals 56 and 66 shown in Fig. IE, is provided with code transmitters which establish the code rates for the master track code. Any type of code transmitter may be used, but for purposes of this description, they are shown and will be considered as being of the relay type which is well known in the art. All such code transmitters are permanently energized, their windings being connected directly between terminals. B and N of the source. These code transmitters, thus energized, operate to open and close their contacts at the preestablished code rate. Such code transmitters are designated by the reference character CT with a numerical prefix which indicates the code rate at which that particular transmitter operates. For example, in Fig. 1A, code transmitter 18tlCT operates to close and open its front and back contacts periodically at the rate of 180 times per minute. Other code transmitters shown have code rates of and 75 operations per minute. Other combinations of code rates may of course be used.

Contacts of the code transmitters, and of other relays which normally follow code, are designated as code following by showing the movable portions as a dotted line in each position to indicate that the contact periodically operates between the two positions, closing front and back contacts alternately. If a code following relay is normally deenergized and operates to follow coded current only on certain occasions, or if certain contacts of a relay are normally non-responsive to code, the movable portion of such contacts are shown solid in the released position, closing back contacts, the energized or code following position, closing front contacts, being indicated by a dotted symbol.

Each track section in the single track stretch and also the main track portion of the station area is provided with two track circuits. Each of these circuits includes a track battery, a track relay, and one or more sets of coding contacts. Each track battery is designated by the reference character TB with a numerical prefix corre-, sponding to the first opposing signal in advance. For example, the track circuit for section 9-12T originating at the west end of this section is provided with a track battery 12TB, the prefix 12 corresponding to the prefix of signal 126 which is an opposing signal for the direction in which the track circuit operates. Where, because of staggered signals, the first opposing signal is more than one track section away, the track battery for the second circuit has the additional prefix A to difierentiate it from the battery of the other track circuit. For example, battery A7TB shown in Fig. 1C is for the eastbound track circuit originating at this location to differentiate it from track battery 7TB in Fig. 1D. Each track relay is designated by the reference character TR, but with a numerical prefix the same as the similarly located track battery. It may also be considered that the prefix of the track relay dwignates the signal which it directly controls, such as track relay 12TR (Fig. 1A) which controls the indications displayed by. signal 12G. Again, the extra prefix A is used when necessary to differentiate between track relays whose circuits operate in series, for example, track relays A8TR and STR.

Track section 912T, for example, has a first track circuit (master code) which controls eastbound traflic which may be traced from the positive terminal of track battery 9TB in Fig. 1B through the winding of series approach relay 10A, normal contact a of code transmitter repeater relay 9TP, one rail of the track section, the

winding of relay 12TR in the direction of the arrow, back contact a of reverse code relay 12RC, and the other rail of the track section to the negative terminal of track battery 9TB. At times, front contact a of relay 12TR bypasses back contact a of relay 12RC in this circuit to hold the track relay energized. The-other or reverse code circuit for the same track section which controls westbound trafiic may be traced from the positive terminal of track battery 12TB over front contact a of distant repeater relay l'lDP, one rail of section 9-12T, reverse contact a of relay 9CTP, the winding of relay 9T R, the second rail of track section 9-12T, back contact a of relay 12TR, front contact b of relay 12RC and front contact b of relay llDP to the negative terminal of track battery IZTB. In this track section, and likewise all other sections, the track circuit connections to the rails are shown conventionally in keeping with the conventional symbol used for the track. The positive and negative markings shown adjacent the rail connections at each end of a particular track section indicate the track leads which are connected to the same rail, like markings indicating like rail connections. It will be understood, however, that the actual polarity of these rail connections may be reversed from section to section for increased safety. For purposes of this specification, code pulses will be considered to be of the positive polarity when the positive terminal of the track battery is connected to the rails over the track lead. When the track battery positive terminal is connected to the rails over the track lead, the code pulses have a negative polarity. i

Each of the other'track sections shown has similar track circuits which may be traced as desired with reference to the two circuits above described. At the present,

however, it is not necessary to trace these circuits as they will be hereinafter discussed in detail. The complete circuits for sections 11*14T and 3-6T, the main track sections at stations X and Z, respectively arenot shown since they do not enter directly into the features of our invention. The portion shown in Fig. 1A for section 11-14T is the end of the track circuits at which plete track circuits are shown. At times in the following description, such a combination will be discussed in order to fully explain the operation of the system.

As previously mentioned, the transmission'of the master code in the track circuit for section 9-12T is controlled by contacts of code transmitter repeater relay 9CTP shown in Fig. 1B. This relay is of the magnetic stick type previously described and is controlled to repeat the code operation of one of the code transmitters at this location. It is to be here noted that as a specific illustration for the system of our invention, we

have chosen the 180 master code rate to control the green aspect, the code rate to control the yellow aspect and the 75 code rate as a carrier for the reverse code when the signals in the master code direction are at stop. A first circuit for controlling relay QCTP at the code rate may be traced from terminal B over normal contact b and the Winding of relay 9CTP, front contact a of home relay 10H, and back contact a of code transmitter 18 9CT to terminal N. It is noted that the flow of current through the relay winding in this circuit is opposite to the direction of the arrow so that the relay contacts are operated to close in their reverse positions. When code transmitter 180CT closes front contact a in its periodic operation, the circuit then extends from terminal B over back contacts ar and an of relay 9TR, front contact a of code transmitter ISOCT, front contact a of relay 10H, and the winding and reverse contact b of relay 9CTP to terminal N. The flow of current through the relay winding is now in the direction of the arrow and relay 9CTP operates its contacts to close in the normal position. these two circuits that, with front contact a of relay 10H closed, relay 9CTP periodically operates its contacts between their normal and reverse positions as the code transmitter 18001 alternately closes its front and back contacts. Back contacts an and or of relay 9TR are included in this circuit to assure that each pulse of reverse code, as will be subsequently described, is terminated so that relay TR is deenergized before normal contact a of relay QCTP is closed to transmit the succeeding pulse of master code. These back contacts of relay 9TR will be included in each of the code rate control I circuits for the code transmitter repeater relay.

- Front contact a of relay 10H selects the 180 code rate to provide a clear indication on signal 12G since relay 10H is energized only when code is being received at this location from the next signal in advance, that is, when signal 106 is displaying any proceed aspect. Another set of control circuits for relay 9CTP may be traced alternately over normal or reverse contact b of the relay, the relay winding, back contact a of relay 10H, front contact b of directional stick relay 10S, and back contact a of code transmitter 120CT to terminal 'N or front contact a of the code transmitter and back contacts an and ar of relay 9TR to terminal B. This It is obvious from i code rate to transmit master code of this frequency to allow a yellow aspect to be displayed by signal 12G for a following move. The circuits for controlling relay 9CTP at the 75 code rate are similar but include back contact a of relay 10H, back contact b of relay 10S, and front or back contact a of code transmitter 75CT. As will appear hereinafter, master code of this frequency acts only as a carrier for reverse code transmitted from the location of signal 12G, this signal displaying a stop indication under these conditions.

The reverse code for section 9-121 is controlled by reverse code relay 1211C shown in Fig. 1A at the location of signal 12G. Relay 12RC is periodically energized over front contact a of track repeater relay 12TP which, in turn, is periodically energized over front contact b of track relay IZTR. It is obvious that, when LETR is energized by a pulse of master code, relay HT? is energized and picks up followed by the energization of relay ll2RC which picks up shortly thereafter. Similarly, the release of relay 12TR at the end of a master code pulse is followed by the cascaded release of relays 12TP and 12RC in that order. The Winding of relay EZRC is snubbed by a resistor to slightly retard its release to improve the reverse code transmission. it is to be noted that, in the beginning of an on-period of a master code pulse, relay KZTR is initially energized over back contact a of relay 12RC as previously described. The closing of front contact a of relay IZTR provides a stick circuit for this relay, bypassing back contact a of the reverse code relay so that, when relay IZRC picks up, relay 12TR is not deenergized until the end of the code pulse. At the beginning of the off-period of the master code, as soon as back contact a of relay IZTR closes, the circuit is momentarily closed over this back contact and front contact b of relay EZRC to transmit the pulse of reverse code, this second track circuit having been previously described. The polarity of this pulse is determined by the position of relay 11D? which is determined, as will be subsequently described, by the traffic conditions in advance of signal 11G.

The choice of three relays to control the application of the reverse code pulses is influenced by the use, in the present system, of relays with mechanically tuned contacts for decoding the frequency of the master code. The arrangement as shown, Fig. 1A, and as above de scribed, is the most economical relay combination that can be used for generating reverse code pulses and for decoding the frequency code, utilizing the relays having mechanically tuned contacts. In other words, the disclosed arrangement requires the minimum number of relays possible to provide both for generating the reverse code and decoding, by mechanically tuned contacts, the master frequency code.

In the system of our invention, frequency code, which is used for the master code, is decoded by circuits which utilize mechanical resonance in place of the well known electrical resonance circuits formerly used. These mechanically resonance circuits are obtained by relay contacts which are mechanically tuned to a selected code rate so that the contacts follow the code pulses only when the preselected code rate is present. At other code rates, these tuned contacts maintain their back contacts closed. Such relays, as previously mentioned, are disclosed and claimed in the aforementioned Hufnagel patent. in one form of the relay as shown by either relay ZZTR or 12""? in Fig. 1A, two non-tuned code following contacts are provided which alternately close front and back contacts during the reception of any code rate. In addition, one mechanically tuned contact having a preselected code rate is provided. Such contacts are conventionally designated in the drawings, as illustrated by contact 6 of relay EZTR, by a line drawn through the terminal of the movable portion of the contact and a numerical designation indicating the code rate to which the contact is tuned. Thus contact c of relay LZTR is tuned to the 180 code rate so that front and back contacts are alternately closed only when the relay is ener gized by current coded at this rate. As previously described, contacts a'and b operate when relay 121?. is energized at any code rate. Relay 12TP is similar in construction but its contact c is tuned to the code rate so that it alternately closes back and front contacts only when the relay is energized by current pulses at the 120 code frequency.

The decoding circuits shown in Fig. 1A allow for the decoding of each of the three code rates used herein, that is, 180, 120, and 75 pulses per minute. The recep tion of code is detected by the distant track repeater relay IZDTFP which is energized over tuned front contact c of relay 12TR. As previously mentioned, front contact 0 is closed periodically only when relay 12TR is energized by code pulses at the 180 code rate. Relay IZDTFP is thus periodically energized and is snubbed by a half-wave rectifier unit so that it is sufficiently slow release to bridge the open-circuit time of front contact c of relay 12TR. During the reception of 180 code, the code detecting relay 12CD is also energized. During the oif-period of each code cycle, capacitor C1 is charged from terminal B over back contact 0 of relay 12TR, back contacts. 0 and b of relay 12TP, the latter contact being non-tuned, and through capacitor C1 and resistor R1 to terminal N. Since relay IZTP repeats the operation of relay IZTR, its front contact b will be closed during the on-period of the code cycle for any code rate. At this time, relay 12CD is energized, by the charge stored in capacitor C1, over front contact b of relay 12TP in an obvious manner. The half-wave rectifier connected in multiple with the relay winding provides sufficient slow release time so that relay IZCD likewise remains picked up with its front contacts closed during the off-period of the code cycle. This arrangement for energizing relay 12CD assures that each of the tuned relay contacts is properly operating before the capacitor can be charged and subsequently energize the relay. Home relay 12H is steadily energized by a circuit including front contact a of relay TZDTFP and front contact a of relay 12CD during the reception of master code of the 180 code rate.

If code pulses at the 120 code rate are received by relay 12TR and repeated by relay 12TP, relay 12H is energized by a circuit from terminal B over back contact 0 of relay 12TR which remains closed under these conditions, front contact 0 of relay 12TP which periodically closes at the 120 code rate, front contact a of relay 12GB and the winding of relay 12H to terminal N. It will be remembered that relay 12CD is energized and picks up during reception of code at any rate. Thus relays 121-1 and 12CD are energized and pick up during the reception of 120 code. If 75 code rate pulses are received by relay IZTR, it is obvious that, under these conditions, only relay 120D will be energized and pick up to close its front contacts.

It is not necessary to decode master code of the 75 code frequency at intermediate signal locations such as signal 8G (Fig. 1C). Thus decoding circuits shown in Fig. 1C for track section 7-81" only detect code of the 180 and the 120 code rates. In this track section, master code at the 75 code rate is used only as a carrier for the reverse code, for reasons to be discussed hereinafter, and has no bearing upon the aspect displayed by signal 80 or upon the code being transmitted into the section to the rear. At signal 12G, it is necessary to decode master code of the 75 rate in order to provide overlap control for the eastbound station entering (home) signal 146, Fig. 2, as will be apparent hereinafter.

Track relay STR and its repeater relay STP are similar to relays TZTR and 121"? previously discussed. That is. relay 8TR is provided with two code following contacts a and b which are non-tuned and thus follow any code rate and with a tuned contact which is mechanically resonant at the 180 code rate and thus responswe only to I Relay l lHTFP is energized when 7 reverse code is received over a circuit including'backco'n;

code pulses at this rate to close its front and back con-f I tacts periodically. Relay 8TP has non tuned contacts a and b and tuned contact c which is responsive only to code of the 120 code, rateg However, an additional front contact repeater relay, of the track relay is provided at this location for code detection. Relay STFP is energized, during the reception of any coded track current over front contact b of relay STP. Relay 8TFP is made slow release by the capacitor-resistor combination connected in multiple with the relay winding so that it will remain picked up with its front contacts closed during the elf-period of the code cycle, 1

Duringthe reception "of master code of the 180 code rate distant track repeater relay SDTFP is energized "Weracircuit including front contact c ofrelay STR which is periodically closed under these conditions. Relay SDTFP is snubbed by a half-wave rectifier and is thus sufiiciently slow release to bridge the open circuit time of front contact 0 of relay STR. Under the same conditions, home relay 8H (a back contact track repeater) is energized by a circuit including back contact cof relay STR, back contact 0 of relay 8TP, front contact a of relay SDTFP, front contact a of relay STFP, and, the winding of relay 8H. Relay 8H is provided with a halfwave rectifier snub which is connected in multiple with the relay winding under these conditions, over front contacts a in series, of relays STFP and BDTFP. 'Ihus relay 8H, as long as 180 code is being received by relay STR, is made sufiicient-ly slow relase to bridge the open circuit time of back contact 0 of relay STR. As soon as relay 8DTFP or relay 8TFP releases, at which time the supply of coded current is interrupted and the snub re moved, relay 8H quickly releases. If master code of the 120 rate is being received, the periodic closing of front contact 0 of relay 3T]? energizes home track repeater relay SHTFP which picks up and remains with its front contacts closed during normal coding action. Under these conditions, relay 8H is energized and the snubbing circuit completed over front contacts aof relays- SHTFP and 8TFP. Relay 81-1 is repeated by a slow release relay 8HP, energized over front contact 1: of relay 8H.

Each of the signal locations at which master code is received by the track relay is provided with one or the other of these two forms of decoding circuits for the frequency code using the mechanically tuned relay contacts to detect the various code rates. Each of these 10- cations will be fully discussed during the description of the system operation hereinafter and will not be further described in detail at the present time.

The polar reverse code of this system is decoded using non-tuned relay circuit arrangements. A specific example is shown in Fig. 1A by the decoding circuits associated with track relay 11TR. The relays in this arrangement are the distant track repeater relay llDTFP, the home track repeater relay llHTFP, and the home relay 11H. When positive polarity reverse code is received at this location by relay llTR, relays IIDTFP and 11H are energized and picked up. The circuit for the former of these two relays is traced from terminal B over front contact bn of-relay llTR and the winding of relay llDTFP to terminal N. This latter relay is energized periodically each time front contact bn of the track relay closes and is sufficiently snubbed by the resistor-capacitor combination connected in multiple with its winding to hold its front contacts closed during the elf-period of the reverse code. Relay 11H is then energized over a circuit including back contacts lm and br, in series, of track relay llTR and front contact a of relay 11DTFP. Relay 11H is snubbed by a h-alfwave rectifier as long as front contact a of relay llDTFP remains closed so that relay 11H is sufficiently slow release to retain its front contacts closed during the open circuit time of the track relay back contacts.

tact bit and front contact hr of track relay llTR. Relay IIHTFP is similarly snubbed by a resistor-capacitor combination so that it remains with itsfront contacts closed during the off-period of the reversecode. Under these conditions, the circuit for relay 11H is completed over front contact a of relay HHTFP. A rcpeaterof the home and distant track repeater relays, relay 11DP, is energized by a circuit traced, from terminal B over front contact a of relay 11H, front contact c of relay llDTFP, and the winding of relay -11DP to terminal N.

Relay llDP is thus energized when positive reverse code is received by relay 11TR. Relay 11DP, by its contacts a and b, acts to pole change the reverse codesupplied 'Ilhese modifications and ;the reasons therefor be discussed more fullyhereinafter in connection fwith'the system operation.

.Any A.P.B. signal system uses directional stick relays to establish the direction of traffic for following train moves. Such directional stick relays are usually provided only at intermediate signal locations, one being associated with each signal for a particular direction of traffic and becoming energized upon the passage of a train past that signalin the controlled direction. The system of our invention requires the simultaneous occupancy of the track section to the rear of the signal (the section in approach to the signal) and the track section in advance of the signal in orderto energize the associated stick relay. Two forms of circuit arrangement to accomplish this energization of the stick relays are necessary. The first method for energizing the directional stick relay utilizes a series approach relay for the track section to the rear of the signal and a series approach relay forthe section in advance of the signal; Each of these relays must be energized and pick up before the stick relay can be energized. 'Ilhe second form requires that a series approach relay in the track circuit to the rear of the signal be energized and a code detecting relay for the section in advance of the signal be deenergized before the stick relay is energized. In each of these forms, it is obvious that the track section to the rear and the track section in advance must be occupied for the required conditions to be in effect. The first form is illustrated in Fig. 1D for westbound traflic at signal 7G. The second form is illustrated at signal location 8G in Fig. 10. Each formof the circuit arrangement will be discussed in detail in the following paragraphs.

Referring now to Fig; 1D, westbound signal 76 is one of a staggered pair of intermediate signals, 7G and 86. At this location, reverse code is received from the .west through the rails of track section 7-8T. fromthe. apparatus associated signal 8G. In track section 5-7T to the cast, that is, to the rear of signal 76, master code is transmitted from this location to the headblock I signal 56 and reverse code is received from the east. Master code is, of course, transmitted westthrough the rails of section 7-8T in accordance with the tratfic conditions to the east. in both directions from this signal location. in the track circuit for the master code in section S-7T is a series approach relay 7A which obviously is in series :negative polarity Thus, 'master code is transmitted Inserted" pick up and close its front contact a periodically inaccorclance with the code rate of the master code. Relay 7A is repeated by relay 7AP which is energized through an obvious circuit including front contact a of relay 7A. Relay 7AP is snubbed by the resistor-capacitor arrangement in multiple with its winding so that once it has closed its front contacts, it retains these contacts closed during the off-periods of the master code.

In series with track battery 7TB, which supplies track current to the master code track circuit for section '73T, is the series approach relay 7AA. This relay operates in a manner similar to that described for relay 7A so that upon the near approach of a train, sufficient track current flows to operate relay 7AA and it periodically closes its front contact a in keeping with the master code rate. The repeater relay 7AA? is energized over front contact a of relay 7AA and is snubbed to have sufficient release time that its front contacts remain closed during the off-period of the master code. Each of these series approach relays may be so adjusted that they will begin operation, as a specific example,-.-when an approaching train is within about 2000 feet of the signal location. It is obvious, of course, that when a westbound train passes signal 76, relay 7AA immediately begins to operate since the train shunt of section 7- T is in the immediate vicinity of the signal itself.

During the approach of a westbound train through track section -7T, master code is supplied at a predetermined rate, in accordance with the indication displayed by signal 7G, to the track circuit. When the train approaches within a short distance of signal '76, relay 7A is operated by the master code current flowing from track battery ASTB and periodically closes front contact a to energize relay 7AP which retains its front contact closed. At this time, with signal 7G displaying a proceed indication, master code at the 75 code rate is transmitted through track section 78T and reverse code of a selected polarity is received by relay 7TR. With reverse code being received, relay 71-1 is energized through the decoding circuits, in a manner previously described, with relay 7DTFP or relay '7HTFP also energized. As the train passes signal 76 and shunts track section 78T, relay '7CTP continues to supply coded energy to the rails. This results in the operation of relay 7AA by this coded current which is of sufficient level to operate the relay. The periodic closing of front contact a of relay 7AA energizes its repeater relay 7AA? which picks up to close its front contact.

The release of relay 7TR interrupts the decoding circuits as does the opening of back contact b of relay 7AAP. However, a momentary circuit is completed to energize directional stick relay 78 at this time. This circuit extends from terminal B at front contact a of relay 7AP over front contact a of relay 7AAP, front contact a of relay 7H, and the winding of relay 78 to terminal N. Relay 75 picks up and closes its front contact a to complete an initial stick circuit which bypasses front contact a of relay 7H. Relay 7H, of course, is deenergized by the interruption of the decoding arrangement and releases shortly but not before relay 7 S picks up. The closing of back contact a of relay 7H completes a final stick circuit for the directional stick relay which includes back contact a of relay 7H and front contact a and the winding of relay 78. During this energization of relay 78, front contacts a of relays 7AP and 7AAP remain closed for a sufficient time to maintain the initial stick circuit until back contact a of relay 7H closes. This initial stick circuit is closed sufficiently long enough to provide a high degree of protection against the failure of the stick relay to pick up and hold, even though the westbound train is very short and moving at high speed. if signal 86 was located at the same place as signal 76, that is, as a double signal location, a directional stick relay 88 associated with signal.8G would be similarly controlled for an eastbound train movement.

However, with signal 86 located at a separate locatron, t he control of directional stick relay SS is of the other'formf That is to say, relay SS is energized in response to the energization of a series approach relay for the rear track section and the deenergization of a code detector for the track section in advance of the signal. Referring to Fig. 1C, a circuit may. be traced for energizing relay 88 from terminal B at frontcontact a of series approach repeater relay 8AP over backbontact b of relay 8TFP, front contact a of relay SHP, and the winding of relay to terminal N. Relay SAP is energized over an obvious circuit including front contact a ofseries approach relay 8A. This latter relay begins to follow the master code current transmitted westward in section 8-101 when an eastbound train approaches within the preselected distance of the signal. Relay 8A1, of course, is snubbed so as to be sufficiently slow release to hold its front contacts closed during the olfperiod of the master code. Relay STEP, which is energized over front contact 12 of relay STP, is energized and remains picked up when track relay STR is receiving master code of any of the three code rate, as has been previously described. Relay 8TFP thus is responsive to the occupancy of section 7-8T by an eastbound train as soon as it passes signal 8G. In order for the train to proceed, signal 36 must be displaying either a clear or an approach indication so that home relay 3H and its repeater relay 8HP are energized. Thus, at the instant the eastbound train passes signal 8G displaying a proceed indication, relay SAP will be picked up due to the approach of the train through the rear track ection. Track relay front contact repeater STFP will release shortly after the occupancy of section 7-8T, but home repeater relay iii-ll, which is inherently slow release, will maintain its front contact closed. Thus relay SS is energized momentarily as soon as the train passes the signal and picks up to close its front contact a to complete an initial stick circuit. A final stick circuit is completed when home relay 8H? releases to close its basic contact (1. However, the initial stick circuit provides sufficient energization of the relay so that it will remain up until the final stick circuit is completed.

Referring now to Fig. 1B, we shall discuss the control of the directional stick relays 9S and at this double signal location. Both forms of control are represented by the circuits for these relays. However, special provisions must be made to assure the energizetion of .both series approach relays for the control of relay 95. It is to be remembered that, under normal conditions, master code is transmitted westward from this signal location through track section 9-12T while reverse code from the headblock signal location 126 is received over the rails of the same track section. In track section 8-101, master code is received at this location by track relay ltiTR while reverse code is transmitted eastward by the operation of reverse code relay NRC. Series approach relay 10A in series with track battery 9TB in the master code track circuit for the westward track section is thus controlled in the usual manner upon the approach of the train within, as a specific example, 2000 feet of signal ltlG. At that time, relay 10A follows the master code pulses, periodically closing its front contact a to energize its repeater relay 10AP which picks up and holds its front contact closed because of its slow release characteristics due to the resistor-capacitor snub.

Series approach relay 9A is connected in series with track battery ltlTB only when a westbound train occupies track section 8-10T, this circuit being completed by the release of front contact track repeater relay 101" PP. This relay detects the code following operation of the front contacts of track relay NTR through the operation of the direct (code following) repeater relay 10TP to periodically close its front contact b. Relay 10TFP thus detects the reception of any code, being picked up and 13 holding its front contact closed when relay IOTR operates to follow any code frequency. When track section 8-10T is shunted by a westbound train so that track relay 10TR is deenergized, relay ltlTFP releases and its back contact e connects relay 9A in series with track battery '10TB. However, under these conditions, with no master this location eastward through the track section.

-A special circuit is therefore provided to energize relay 10RC at the 120 code rate, during the approach of a westbound train, so that series approach relay 9A may be energized. This. circuit for relay 1011C may be traced from terminal B over front contact of home relay 9H,

which indicates that signal 9G is displaying a proceed indication, back contact 12 of relay IOTFP which is closed when the westbound train occupies the track section, front contact b of code transmitter IZOCT, which is periodically closed at the 120 code rate, and the 'wind ing of relay RC to terminal N. Track circuit current is thensupplied through a circuit traced from the positive terminal of track battery ltlTB, over back contact e of relay 10I'FP, the winding of relay 9A, and front contact a of relay 9H to one rail of the track section, returning from the other end of the section over the other rail of the track section, back contact a of relay 10TR, front contact b of relay 10RC which at this time is periodically closed at the 120 code rate, and back contact b of stick relay 98 to the negative terminal of track battery 10TV. When the westbound train approaches within the preselected distance of signal 96, relay 9A is sufliciently energized to follow the master code pulses and its repeater relay 9AP is periodically energized over front contact a of relay A. Relay 9AP, the winding of which is snubbed by a resistor-capacitor. combination, holds its front contacts closed as long as relay 9A follows the code pulses.

Directional stick relay 98 is thus energized in the same manner as that previously described for stick relay 78 (at signal 76), that is, by the energization of a series approach relay for the track section to the rear of the ;signal and the energization of the series approach relay for the track section in advance of the signal. 'Thus, at the instant the westbound train passes signal 96, a circuit is established for energizing directional stick relay 98 which extends from terminal B at back contact d of home repeater relay 10I-IP which is deenergized prior to this time over front contact a of relay 9AP, front contact a of relay 10AP which closes shortly after the train occupies section 9-12T, front contact d of home relay 9H which remains closed for a short interval after track section is occupied, back contact 0 of relay 108 to check that the opposing stick relay is not energized, and the winding of relay 98 to terminal N. Relay 98 picks up to close its front contact a which bypasses front contact d of relay 91-1 to establish an initial stick circuit for relay 95. Upon the subsequent release of relay 9H, the closing of its back contact d establishes a final stick circuit for relay 98 including this back contact d, front contact a 1 of relay 9S, and back contact 0 of relay 103. This final stick circuit remains effective until relay 9H is again energized upon the reception of reverse code when the I train clears section 9-12T.

Directional stick relay 108 is controlled in a manner similar to the control of relay 88 at signal 86, although section 810T, front contact b of relay 10HP.whic h is still closed at this time, back contact a of relay 9AP, front contact a of relay IOHP, back contact 0 of'relay 9S, and thewinding of relay 108 to terminal N.; The contacts of relay IOHP are included in this circuit rather than contacts of home relay 10H because the latter relay will release more quickly. due to the interruption of its snub circuit upon the release of relay 10DTFP or relay 10HTFP. Relay 10H]? is sufficiently slow release to hold the energizing circuit closed until relay 10S picks upand closes its front contact a to complete an initial stick circuit. I The final stick circuit of relay 108 may be traced from terminal B over back contact a of'relay .10HP, front contact a of relay 108, back contact 0 of relay 9S, and the winding of relay 108 to terminal N. The

winding of relay 108 is shunted by a resistor to bridge the V release transfer time of independent front and back contacts of relay 10HP. This is necessary. since front contact b of this relay is in the initial stick circuit of relay 10S and will open before back contact a can close to complete the final stick circuit.

The apparatus and"circuits at the various signal locations, which have thus far been discussedin detail provide a signal system for the stretch of single track having signal control limits as shown in Fig 2. Referring now to Fig. 2, it is evident that the stretch of track shown extends in each direction beyond the limits of the track shown in the various parts of Fig.'l taken together.

The stretch of track is extended in Fig. 2 for the purpose of better and more simply illustrating the limits of the signal controls which are effective for various types of train movements. The control limits illustrated in a conventional' manner above the track diagram by solid and dotted lines are for westbound train movements, that'is, are for the signals governing westbound train movements' The similar limits shown below the track diagram are for the signals governing eastbound movements;

The signals along the portion of the track in Fig. 2 which corresponds to the track shown in the parts of Fig. 1

of the system, that is, when no train occupies any porlished for energizing relay 103 which extends from termi- I 'relay IOTFl which releases when the train occupies track tion of the stretch shown. signal control limits and for the track code are shown in the legend at the bottom of Fig. 2 and it is believed that they can be completely understood from this legend.

The study of the diagram in Fig. 2 shows that the 7 control of the headblock signals for opposing moves, for the approach and the clear indications, extends to'the opposing headblock signal.

station Z, which controls westbound moves leaving the station and entering the single track stretch between station Z and station X, is controlled to the stop position when an eastbound train passes signal 12G as is indinal 12G, signal 56 stands in its clear position.

passes signal 56. At the same time station entering'signal 146 at the west end of station X is controlled to its approach position, displaying a yellow aspect. Signal 146 is controlled to its stop position displaying a red aspect when the same westbound train passes sign al'y9G;.

the distant signal for station X. Similar conditions hold for station entering signal 36 at the east end of station Z, except that this signal is controlled to its stop indication when an eastbound train passes the location of signal 76 rather "than signal 8G, signals 7G and 86 being locatedon a normal stagger.

The symbols used for-the I This same control is also g true for the intermediate signals in advance of a head block signal as far as the opposing headblock signal for a single track stretch. As an example, signal 5G at For a'followingmove, station entering signal 14Gremains in its stop position until the preceding trainpasses signal G at which time signal 14G is controlled directly to its clear position. As shown in Fig. 2, signals 1G and 2G east of station Z are placed in what is generally termed a reverse stagger. Such location of signals is used depending upon speed restrictions, grades, or other factors to best control the movement of trains. With signals 1G and 2G so located, station entering signal 6G at station Z is controlled to its approach position for a following move when the preceding train passes the location of westbound signal 16. Signal 66 is not held at stop until that train passes signal 26, since the controlling factor, for station overlap purposes, is that only the track sections between signal 6G and the second opposing signal in advance must be unoccupied. Signal 66, however, is controlled to its clear position for a following move only after the preceding train has cleared the second eastbound signal in advance, signal 2G. Other signal control limits and the flow of the various code pulses is obvious from the above discussion and with an inspection of the drawing. Such signal control limits are not unique to the system of our invention and Fig. 2 is provided primarily as an aid to understanding the description of the operation of the system which follows.

We shall now describe the operation of the apparatus in the system of our invention during the movement of an eastbound train and then a westbound train through the stretch of single track shown in the parts of Fig. 1. As shown, the apparatus in Fig. 1 in its entirety is in the normal or at-rest position, that is, the position it assumes when no train is occupying any track section between the stations X and Z, or closely approaching such sections.

For section 9-12T, relay IZTR is following the master code pulses transmitted from the eastern end of the section by relay 9CTP as supplied by track battery 9TB. These code pulses are at the 180 code rate so that relays lZDTFP and lZCD, shown in Fig. 1A, are energized and held picked up due to the coding action of relay 12TR and its repeater relay 12TP through the mechanically tuned frequency responsive contacts of these relays. In addition, relay 12H is energized over front contacts a of relays 12DTFP and IZCD and is likewise picked up. Signal 12G is thus displaying a green aspect to give a clear indication to approaching trains. The green lamp G of signal 12G is lighted over the circuit including front contacts b, in series, of relays 12H and IZDTFP.

At the same time, transmitting relay 11CTP is energized at the 180 code rate through circuits including normal and reverse contacts b of relay 11CTP alternately, front contact b of relay l2CD, front contact a of relay 121-1, and back contact a of code transmitter ISDCI or front contact a of this transmitter and back contacts an and or of track relay llTR. Thus, code pulses at the 180 code rate from track battery llTB are transmitted west through the main track section 1114T. At the same time, reverse code pulses of positive polarity are received from the west end of this track section by relay llTR.

Likewise, relay IZRC is energized periodically at the 180 code rate over front contact a of relay l2TP so that reverse code pulses are transmitted eastward through section 9-121" by front contact b of relay 12RC, this reverse code being of the positive polarity since relay 111)? is energized and its front contacts a and b are closed at this time. At the eastern end of section 9-121, the normal armature of relay 9TR is responsive to the positive polarity reverse code so that its contacts periodically pick up. This results, through the decoding arrangement previously described, in the energization of relays 9DTFP and 9H. This decoding arrangement includes back contact b of relay 10AP which is released at this time since relay 16A is not responsive to the coded energy flowing in the track circuit. The circuit for relay 9H.also includes back contact dof directional stick relay 1&8 which likewise is closed since no train haspassed in an eastbound direction. Signal 96 thus displays a .green aspect to provide a clear indication for westbound trains, the circuit for the green lamp G of signal 96 including front contacts b, in series, of relays 9H and 9DTFP. It is to be understood that this signal lamp may be approach lighted upon the entry of a westbound train into track section 8-10T in a well knownmanner,

'but for simplicity such approach lighting circuits are not shown in the present disclosure.

In section 849T, at the west end, track relay 10TR follows code pulses at the 180 code rate transmitted from the east end. At this time, of course, relays 9A,-9AP, and 98 are all deenergized and released. Thus, a circuit is completed over back contacts d and b of relays 9S and 9AP, respectively, for the decoding arrangement, similar to those previously described, by which relays lttDTFP and NH are energized and pick up. Signal 19G thus displays a green aspect, its lamp G being energiz'ed by a circuit including front contacts b of relays ltlDTFP and NH. Relay ltll-IP, a slow release repeater of relay 19H, is likewise energized since front contact 0 of relay 10H is closed.

As previously indicated, relay ltlTP follows the code operation of relay 10TR, that is it operates at the 180 code rate, and periodically closes its front contact b to energize relay ltlTFP which picks up and having slow release characteristics, holds its front contacts closed during the off-period of the code pulses. With relay 9H picked up closing its front contact c, and with front contact I) of relay 10TH closed, relay NRC is periodically energized over front contact a of relay 10TP and follows the code pulses to transmit, over its front contact b, a reverse code of positive polarity through the track rails. Other circuits governing relay IORC are open at this time.

At the eastern end of the track section at the location of signal SG, relay A7CTP is operated at the 180 code rate in order to transmit the master code from track battery AVTB. During the off-periods of this master code, the normal armature of track relay A7TR is responsive to the reverse code flowing from the west end of the circuit and operates its contacts accordingly. Relay 8A is nonresponsive to the master code since the track section is unoccupied and thus relay SAP is deenergized and released. Back contact b of relay SAP completes the connection to the source of energy for the decoding circuit arrangement including contacts bn and 'br of relay A7TR and relays A'7DTFP and A7H are energized at this time. The circuit for relay A7H checks over back contact c of relay to assure that this relay is released. Since this location is only a repeater for the reverse code, that is, the decoding relays do not directly control a signal, a check is included in the circuit for relay A7DTFP and for relay A7I-ITFP over back contact c of the opposite polarity decoding relay to assure that the decoding action is proper. In addition, the capacitor-resistor snub for each relay is connected in multiple with the relay winding only when back contact 0 of the other relay is closed. When a change occurs in the polarity of the received reverse code, the capacitor snub of the released relay is charged by the code following action of the corresponding armature of relay A7TR. For example, if the conditions shown in the drawings change so that negative reverse code is received by relay A7TR, the capacitor snub associated with relay A7H TFP is periodically charged over front contact hr of the track relay although relay A7HTFP is not energized because back contact 0 of relay A7DTFP is open. When the originally energized relay (A7DTFP in the specific example) releases at the end of its slow release period, the closing of its back contact 0 allows the charge on the capacitor to immediately energize the opl7 posite relay (A7HTFP) which quickly picks up. This provides a quick pole changing action of the reverse code repeated into the eastward track section. in track section 7-8T, relay 7CTP at the eastern end is periodically energized at the 180 code rate through a circuit which is obvious from the inspection of the drawings by considering the previously traced circuits for similar relays. Contact a of relay -7CTP transmits pulses of master code at the 180 code rate through the rails of the section so that relay 8TR at the west end follows the code pulses and is repeated in the usual manner 'by relays 8TP and SRC. The circuit for relay 8RC is completed over front contact a of relay A7H to assure that reverse code is being received through the section to the rear of signal 8G. Relay 8RC periodically closes its front contact b to transmit positive polarity reverse code through the rails which the normal armature of relay 7TR at signal location 76, follows. At the west end of this section, because of the code following action of relays STR and 8TP, relays STFP, 8DTFP, and 8H are energized through the various decoding circuits and hold front contacts closed, having slow release characteristics due to the snubs on the relay windings. The green lamp G of signal 8G is thus energized over front contacts b of relays SDTFP and 8H and a clear indication is displayed. At the east end, relay 7AA is obviously nonresponsive to the master code pulses since the section is unoccupied and, therefore, relay 7AAP is deenergized and in its released position. With back contact b of relay 7AAP closed, terminal B is connected to the decoding arrangement for the reverse code and, with positive' polarity reverse code pulses being received, relays 7DTFP and 7H are energized and pick up. Signal 7G thus displays a clear indication since its green lamp is energized over the circuit including front contacts b of relays 7H and 7DTFP. Both stick relay connected with the two signals, that is, relays 7S and 88, are deenergized at this time and in their released position. At the west end, relay 8HP, a slow release repeater of home relay 8H, is energized over front contact c of relay 8H.

relay, 5CD to assure that a code is being received from I over the circuit including front contacts b of relays GDTFP and 6H.

It is now assumed that an eastbound train passes signal 126 which is displaying a green aspect. The rails of section 912T are shunted and relay 12TR is thus deenergized and remains released with its back contacts closed. The decoding relays IZDTFP, 120D, and 12H all release at the end of their slow release periods, with relay 12H releasing very shortly following the release of relay 12CD since its snubis interrupted by front conmission of reverse code from this location is halted. It

is obvious that reverse code pulses would also be shunted by the train occupying the section.

It is apparent from Fig. 2 that the approach of this train toward station X causes changes in the condition of the apparatus associated with the stretch of track be- In section 5-7T, the eastern section of the single track stretch, relay ASCTP, shown in Fig. 1D, is periodically energized over the usual circuit arrangement with the 180 code rate being selected over front contact 0 of relay 7H. Coded operation of contact a of relay A8CTP transmits master code pulses which relay STR at the eastern end of the section follows. This code following operation of relay 5TR causes its repeater relays 5TP and 5R0, each a direct front contact repeater of the preceding relay, to likewise operate at the 180 code rate. The periodic closing of front contact b of relay SRC transmits a reverse code having the positive polarity, as established over front contacts a and b of relay 6DP, which controls the normal armature of track relay ASTR at the western end of the track section. Since relay 7A is non-operating and relay 7AP thus deenergized, the reverse code decoding arragement is completed over back contact b of relay 7AP and the operation of contact bn of relay ASTR periodically energizes relays ASDTFP and ASH so that these relays pick up. The circuit for relay A8H is checked over back contact 0 of stick relay 78. At the eastern end, the coded operation of the mechanically-tuned, frequency responsive contact c of relay STR and ordinary contact b of relay STP results in the energization of relays SDTFP and 5CD in the usual decoding arrangement. In addition, relay 5H is energized overfront contacts a of relays SDTFP and 5CD. Signal 56 thus provides a clear indication for westbound trains, its green lamp being lighted by an obvious circuit including front contacts b of relays 5H and SDTFP.

Relay 6TR is operating at this time to follow code pulses of the 180 code rate received through the rails of section 3-6T from the eastern end. Relays 61? and 6RC repeat the operation of the track relay, the circuit for relay 6RC being completed over front contact b of tween stations X and Z to indicate the approach of the train by changes in signal indications. However, in order to simplify the description, these changes are for the moment ignored and the apparatus considered to be in the at-rest condition in which it was last described. This assumption does not affect the understanding of the operation of the system. As the description progresses, the changes which occur at station X will become apparent from the description of the operation of the apparatus in the vicinity of station Z, particularly the change in the indications displayed by signals 3G and 1G (Fig. 2).

With section 9-12T occupied, relay 9TR is also deenergized and all its contacts remain in their released position. With front contact bn. of relay 9TR remaining open, decoding relay 9DTFP is deenergized and releases at the end of its slow release period. Relay 9H releases shortly following the release of relay 9DTFP since its energizing circuit and'rectifier snub are interrupted by the opening of front contact a of relay 9DTFP. Relay 9CTP continues to follow the code transmitter since its operating circuit is not affected by the passage of the train into section 9-12T. In other words, the release of relay 9TR to continuously close its back contacts does not interfere with the operation of code transmitter repeater: relay 9CTP. However, the release of relay 9H and the resultant opening of its front contact cdeenergiz'es relay 10RC so that itno longer follows the operation of relay 10TP. This halts the transmission of reverse code from this location eastward through track sec- I 7 tion 8-10T. Release of relay 9H also changes the indicain track section 8-10T deenergizes track relay A7TR and its contacts remain in their released position. This results in the release of the decoding relays A7DTFP and A7H. The opening of front contact a of relay A7H interrupts the circuit for relay 8RC and this relay no longer follows the code operation of relay STP. The

aera ion section 8-191". With relay '7TR no longer following reverse code, decoding relays 7DTFP and 7H become deenergized and eventually release, opening their front contacts. This controls signal 7G to display the stop indication, the red lamp being energized over back contact I) of relay 71-1.

The release of relay 7H changes the code following operation of relay AECTP to the 75 code rate. The circuit arrangement for controlling the relay at this rate includes back contacts an and ar of relay A8TR, front and back contacts b of transmitter 75CT, back contact [1 of relay 73, back contact of relay 71-1, the winding of relay ASCTP and its normal and reverse contacts b. Reception of master code at the 75 code rate at the east end of track section -7T, of course, causes relays 5TR an STP to operate at this code rate. Contact c of these relays now remain with back contacts closed since each of these contacts is tuned mechanically to be responsive only to higher code frequencies. This causes the release of relay SDTFP and, when its front contact a opens, the release of relay 5H, each of these relays releasing at the end of its slow release period. The release of these relays causes signal 56 to display the stop indication, the red lamp being lighted over back contact I) of relay 5H. However, relay 5CD remains energized since contact b of relay STP follows the 75 code rate, alternately closing front and back contacts so that the decoding action using capacitor C2 keeps the relays sufficiently energized to hold its front contact closed. As long as front contact b of relay 5CD remains closed, relay 6R0 continues to operate to follow the code operation of relay 6TR so that reverse code continues to be transmitted eastward through section 3-6T. However, the opening of contact a of relay 5H de'energizes relay SHP which releases and pole-changes the polarity of the reverse code, the track circuit now being completed over back contacts a and b of this latter relay.

Relay SRC continues to follow the code operation of relay 5TP at the 75 code rate, and the periodic closing of its front contact b continues to transmit reverse code westward through section 5-7T. This reverse code is, at this time, of positive polarity since relay GDP remains energized. At the west end, the normal armature of relay ASTR continues to operate to follow the reverse code. The rate of operation of the relay contacts is immaterial and thus there is no change in the energized condition of the decoding relays. Likewise since front contacts b and a of relays ASDTFP and ASH remain closed, relay 7CTP continues to follow the 180 code rate.

As has been described, each of the westbound signals 9G, 7G, and 5G now displays a stop indication. Meanwhile, referring to Fig. 2, westbound signals 36 and 1G display a yellow aspect, the approach indication. It has been shown that the reverse code transmitted by relay 6RC at station Z eastward into track section 3-6T is now of the negative polarity due to the release of relay SHP. Referring to Fig. 1A, it will be seen that, if relay llTR is energized by negative polarity reverse code so that the reverse armature operates its contacts, relay 11H remains energized, but relay IIHITFP is energized instead of relay llDTFP since back contact bn of relay 11TR remains closed while contact br alternately closes front and back contacts. The yellow lamp of signal 116 is then energized over front contact b of relay 11H and back contact b of relay llDTFP. At the same time, relay 11DI is deenergized by the opening of front contact c of relay llDTFP so that it releases to pole-change the reverse code transmitted eastward from this loca tion, the track circuit being completed over back contacts a and b of relay llDP. At the next signal location to the rear of the westbound signal in the specific example being discussed, relay 9TR, energized by negative polarity pulses, operates the contacts of its reverse armature so that relay 9HTFP is energized instead of relay.

9DTFP, relay 9H remaining energized. Signal 9G thus a 20 displays an approach indication, the yellow lamp being energized over an obvious circuit. The action described for signals 11G and 9G, by way of illustration, corresponds to that which happens under the present conditions at signals 3G and 16 so that they display the approach indication previously described.

As the eastbound train approaches signal 10G, relay 10A is sufiiciently energized to follow the master code pulses being transmitted westward into section 9-12T. This results in the energization of relay 10AP which picks up and holds its front contacts closed. The opening of back contact b of relay 10AP interrupts the energy supply to the decoding circuits for the reverse code at this location. However, relay 9TR is already shunted by the train and has previously ceased operation to deenergize the decoding relays. As the train passes signal 10G, which is displaying the green aspect, track section 810T is shunted causing relay 10TR to be deenergized and remain released. When relay 10TR ceases operation, relay IUDTFP is deenergized and eventually releases. The opening of its front contact a deenergizes relay 10H which likewise releases. This causes signal 10G to display a stop indication immediately behind the train, in fact, as the train passes. Relay 10TP is also deenergized and halts its code following operation. The opening of front contact b of relay IGTP deenergizes relay 10TFP which releases at the end of its slow release period. The circuit is now complete for energizing directional stick relay 105. This circuit is traced from terminal B at back contact 11 of relay 9H over front contact a of relay 10AP, back contact 0 of relay ltJTFP. front contact b of relay 10HP, back contact a of relay 9AP, front contact a of relay 10HP, back contact c of relay 9S, and the winding of relay 108 to terminal N. The closing of front contact a of relay 105, when it picks up, completes an initial stick circuit bypassing front con tact a of relay IOHP. The final stick circuit is completed at back contact a of relay 10H! when this relay eventually releases, deenergized by the opening of front contact c of relay 10H.

A circuit is now complete for controlling relay 9CTP at the code rate. This circuit includes back contact a of relay 10H, front contact b of relay 10S, and front and back contacts a alternately, of transmitter 120CT. When the eastbound train clear section 9-12T, master code at the 120 code rate is immediately transmitted Westward through section 9-12T to the location of signal 12G where relay IZTR operates to follow the code pulses. It is to be noted at this time that, with the sec tion unoccupied, relay 10A is inoperative and relay 10AP is thus deenergized. Relays 12TP and 12RC, of course, follow the code operation of relay 12TR. With these relays operating at the 120 code rate, contact 6 of relay IZTR is inoperative but contact 0 of relay 12TP, which is mechanically tuned to be responsive to this code frequency, alternately closes its front and back contacts. This results in the energization of relays 12H and 12GB, both of which pick up and hold their front contacts closed during this coding action. The circuit is established at this time for energizing the yellow lamp of signal 126, which circuit includes front contact 12 of relay 12H and back contact b of relay 12DTFP.

The operation of relay 11CTP, which has been con- 7 trolled at the 75 code rate until this time is now transferred to the code rate, the circuit being selected over front contact b of relay lZCD and front contact a of relay 12H. This results in the eastbound signal at the West end of section 11-14T changing from the stop indication to the clear indication, its green lamp being energized. This action corresponds to that indicated by the signal control limits shown in Fig. 2.

The operation of relay 12RC to follow the received master code causes reverse code to be transmitted eastward through section 94.21. The polarity of this code 21 is positive since relay 1 1DP is, at this time, energized due to reverse code being received from the west end of station X. These conditions hold providing there is no following eastbound train, which we shall assume. Relay 9TR is properly energized to operate its normal armature, causing code following action by the corresponding contacts. Relay 9DTFP is energized at this time and picks up, but relay 9H remains released, since the decoding circuit controlling relay 9H is interrupted at back contact d of relay 108 which remains energized through its final stick circuit. Signal 9G thus continues to display a stop indication behind the train occupying section 8-10T. H I

As this eastbound train approaches signal 86, relay 8A is eventually sufficiently energized to follow the pulses of master code, and as a result, relay SAP is energized and picks up, holding its front contacts closed. As the train passes signal 86, it shunts the rails of section 7-8T causing the deenergization of relay STR so that itceases to follow code pulses. Relays SIP and STEP are deenergized in order and both release their contacts. Relays SDTFP and 8H are deenergized dueflto the nonoperation of relays ST-R and SIP and these decoding relays shortly release causing signal 8G to change to the stop indication, the red lamp being energized over an obvious circuit. The release of relay 8TFP completes the circuit which was previously traced for energizing directional stick relay 8S and this relay picks up, completing an initial stick circuit at its own front contact a. A final stick circuit is completed when relay 8HP eventually releases at the end of its slow release period closing its back contact a to complete the circuit including front contact a and the winding of relay 85. This latter relay thus holds energized as long as relay SHP is deenergized.

With relay 8H released and relay 8S energized, a circuit is complete for controlling transmitter repeater relay A701? at the 120 code rate. This circuit arrangement is selected over back contact a of relay 8H and front contact b of relay 8S and the relay is controlled over' front and back contacts a, alternately, of transmitter 120CT. Thus, when the train clears section 8-10T, master code at the 120 code rate is transmitted westward to the location of signal 10G. Relay 10TR follows this master code and is repeated directly by the code following operation of relay 10TP. This is followed by the energization of relays IOTFP, 10HTFP, and 101-1. Relay 'IOHTFP is selected since the 120 code operation of relay 10TP permits its contact to be responsive to the code frequency. The circuit is now established for energizing the yellow lamp of signal G, the circuit including front contact b of relay 10H and back contact b of relay IODT F-P, so that this signal displays an approach indication. 7 p

The closing of front contact 0 of relay 10H energizes relay 10HP which picks up open its back contact a, thus deenergizing directional stick relay 108 which releases at this time since its energizing circuit is open at several points. The release of relay 105 to close its back contact b completes the circuit for energizing relay 9H. Since relay 9TR is following the reverse code and relay 9DTFP is already energized so that its front contact a is closed, relay 9H picks up. The closing of its front contact b completes a circuit over front contact b of relay 9DTFP to energize the green lamp of signal 96 and this signal displays a clear indication.

The closing of front contact c of relay 9H completes a previously traced circuit to allow relay 10RC to follow the coding action of relay 10TP and reverse code of positive polarity is transmitted eastward through section 8-10T. The positive polarity for the reverse code is selected by front contact a of relay 9H and back contact b of relay 98 which occupy the named positions at this time. At signal location =8G, the normal armature of relay A7TR follows the positive polarity reverse code.

..' l"he operation of contact, bn ofrelay A7TRperiodica1ly awe though front contact a of relay A7DTFP is closed, relay A7H is not energized since its circuit'is open at back ASH which release.

contact 0 of relay 8S. Relay 8RC is thus prevented from following any code pulses which might incorrectly be received at this time by relay STR. i

As the eastbound train nears signal 76, relay 7AA begins to follow the'master code pulses and relay 7AAP is energized and picks up, holding its front contacts closed. As the train passes signal 76 and shunts the rails of section 5-7T, relay 7A immediately follows the master code pulses transmitted by relay A8CTP. This results in the energization of relay 7AP which picks up and remains held up through the coding action; However, even though front contacts a ofrelays 7AP and 7AAP are closed, relay 78 is not energized since its circuit is interrupted at front contact a of relay7H', this relay having released prior to this time. RelayASTR is deenergized by the train shunting the rails and releases all its contacts. This deenergizes relays A8D'IEP and The closing of back contact a of relay ASH selects contact a ofcode transmitter 75CT to control relay '7CTP, this circuit also at times including back contacts an and ar of relay 7TR. Relay ASCTP continues to operate at the 75 code rate since there is no change in the circuit controlling this relay.

The shunt on section 5-7T deenergizes track relay 5TR so that it no longer follows the pulses of code transmitted into the rails by relay A8CTP at the west end of the section. Relay 5TP is likewise deenergized as are relays SRC and 5CD, the reasons being obvious from an inspection of the drawings. This halts the transmission of reverse code westward into the track section, although of course any code pulses are shunted away from relay A8TR by the train. The opening of front contact b of relay 5CD interrupts the circuit for energizing relay 6RC and this relay ceases to follow the code following operation of relay 6TP. This halts the transmission of reverse code eastward in section 3-6T deenergizing a track relay 3TR at the east end of the track section and causing signal 3G (Fig. 2) to change to the stop indication. This action may be more clearly illustrated by considering relay llTR, shown in Fig.,'lA, which is similarly situated to the assumed relay 3TR. If this relay ceases to follow a reverse code, the resulting release of the decoding relays including relay 11H changes the signal aspect to red, the lamp beingenergized over back contact b of relay 11H. However, it will be noted that there is no change in the reverse code being transmitted eastward through the section to the rear of the home signal, since relay 12RC is controlled directly by track repeater relay 12TP and since relay 11DP was previously released so that the reverse code has a negative polarity. Referring again to Fig. 2, it is apparent from the above that signal 16, the westbound distance signal for station Z, at this time remains at the approach indication.

When the eastbound train clears track section 7-8T, master code pulses are transmitted westward at the 75 code rate by the operation of relay 7CTP. Relay 8TR at the location of signal 8G is responsive to these code pulses to operate its contacts at the same code rate. Relay STP follows directly and, as a result of the periodic closing of its front contacts, energizes relay 8TFP which picks up. However, the decoding relay arrangement is nonresponsive, since neither contact c of relay STR her contact 0 of relay 8T0 operates when the relay is energized at the 75 code rate. Thus relays 8DTFP and SHTFP are not energized. Even though front contactta of relay STFP is closed, relay 8H cannot be energized as its circuit is open at front contacts a of the other two decoding relays. Relay 8RC also remains deenergized since its circuit is open at front contact a of relay A7H which is still deenergized atthis time due to open back 23 contact of stick relay 88. Thus, there can be no operation of relay 7TR at signal location 76 and likewise there is no change in the present conditions to the rear of signal 86.

As the train passes signal 66 to enter station Z, it shunts section 3-6T so that relay 6TR is deenergized, followed by the deenergization of relay 6TP. With both of these relays inoperative, that is, not following code, decoding relays 6D'DFP and 6H are deenergized and shortly released. The closing of back cont-act b of relay 6H energizes the red lamp of signal 6G and this signal thus is controlled to the stop indication. The opening of front contacts a and c of relays 6H and 6DTFP, res'pectively, deenergize's relay 6DP which releases to pole change the connections of track battery TB to the track rails.

When the train clears section 5-7T, the master code being transmitted at the'75 code rate from the west end of this section is received by relay STR. Its operation is repeated, in order, by relays STP and SRC. The periodic closing of front contact b of relay SRC transmits a reverse code, now of negative polarity, westward through the section to the location of signal 7G. The reverse armature of relay A8TR is responsive to this reverse code and operates to follow the code pulses. The periodic closing of front and back contacts hr of relay A8TR causes the energization of decoding relays ASHTFP and ASH, these relays picking up and holding their front contacts closed. Relay 7CTP is now controlled at the 120 code rate, contacts a oftransmitter 120CT being selected over back contact b of relay ASDTFP and front contact a of relay ASH.

The code transmitted westward through section '7-8T is now of the 120 code rate and the operation of relay 8TR changes to follow the new rate. With relay 8T P energized at 120 frequency, its contact 0 alternately closes front and back contacts, causing the energization of relay SHT FP and subsequently the energization of relay 8H. The circuit over front contact b of relay 8H and back contact b of relay 8DTFP energizes the yellow lamp of signal 8G and the signal thus displays an approach indication. The closing of front contact a of relay 3H selects the 180 code rate for controlling transmitter repeater relay A7CTP so that master code pulses transmitted westward are changed to this frequency. The resulting change in the operation of relay IGTR causes, as will be evident, a change in the energized condition of the decoding relays, so that signal 106 now displays a clear indication, its green lamp being lighted over front contacts b of relays 10H and 10DTFP. Relay 8HP picks up to repeat the energization of relay 8H and opens its back contact a to deenergize stick relay 88 which releases. However, the code transmitter repeater relay A7CTP is already controlled over another circuit and the release of the stick relay has no eifect on the coding action at this time. However, the closing of back contact 0 of relay 8S completes the circuit for energizing relay A7H and this relay picks up to complete the decoding of the reverse code being received from the west through sec tion 8-10T. The closing of from contact a of relay A7H completes the circuit for permitting relay SRC to follow the coding action of relay 8TP and the periodic operation of contact b of relay 8RC transmits the reverse code pulses eastward through section 7-8T. This reverse code has a positive polarity as selected over front contact b of relay A7DTFP and back contact b of relay A7HTFP.

Relay 7TR (Fig. 1D) follows this positive polarity reverse code, its normal armature being responsive and in a manner previously described, relays 7DTFP and 7H are energized to decode the reverse code pulses. This energizes the green lamp of signal 7G over an obvious circuit and the signal thus displays a clear indication for west- 24 code transmitter 75CT to contacts of code transmitter 180CT and the master code transmitted eastward through section 5-7T is changed to the 180 code rate. Operation of relay STR at this new code rate causes the energization, through the decoding circuit network, of relays SDTFP and 5CD in the previously explained manner. This is followed by the energization of relay 5H over front contacts a of relays SDTFP and 5CD. Signal 5G thus displays a clear indication, its green lamp being energized over an obvious circuit. It is to be noted that relay 5CD of the decoding combination may be picked up first when 75 code rate pulses are originally received as the train initially clears section 5-7T. However, this pickup of relay 5CD is immaterial to the operation of the system. It is to be further noted that, at this time, the reverse code transmitted as a result of the operation of relay 5RC is still of a negative polarity so that there is no change in the code being transmitted westward towards the location of signal 86 and this signal remains at the approach indication.

When the train clears section 3-6T, that is, leaves completely station Z, master code at the 75 code rate is received through section 3-6T and operates relay 6TR. However, 75 code operation of relays 6T R and 6TP does not affect the decoding circuit arrangement since contacts 6 of these two relays are mechanically tuned to other code rates and thus do not operate. The three decoding relays remain released at this time and there is yet no change in the released condition of relay 6DP which causes negative polarity reverse code to be transmitted westward. Referring to Fig. 2, when the train is completely past the westbound signal 1G, the master code transmitted westward is at the 75 code rate similar to the action caused in section 7-8T when the eastbound train cleared past signal 7G. However, referring to Fig. 1A, it will be noted that, if pulses at 75 code rate are received by relay 12TR, relay 12CD is energized and picks up, transferring the control of relay 11CTP to transmitter 120CT so that the control of relay ASQTP is shifted from contacts of master code in the section to the west changes to the code rate. Similar action occurs at the east end of station Z so that, after the train has cleared past signal 1G, 120 code rate pulses are received through section '3-6T by relay 6TR. The repeating operation of relay 6TP at the 120 code rate causes relay GHTFPto become energized followed by relay 6H and these two relays pick up. Signal 6G thus changes to the yellow aspect or approach indication at this time. However, relay 6DP remains deenergized since its circuit is open at front contact 0 of relay 6DTFP.

After the train has moved east of signal 26 (Fig. 2), code pulses at the code rate are received through section 36T resulting in the energization of relay 6DTFP rather than relay =6HTF P, changing the indication of signal 6G to clear. Also, relay GDP is energized at this time and picks up to pole-change the track circuit connections to battery 5TB so that the reverse code in section 5-7T is now of a positive polarity. The resulting change in the energized combination of the decoding relays at signal 7 G transfers the master code in section 7-8T to the 180 code rate. At the west end of section 7-8T, this code rate change transfers the decoding relay arrangement to control signal 86 to display a clear indication. The apparatus for the single track stretch between stations X and Z is now returned to its normal at-rest condition as shown in the various parts of Fig. l and the system is now ready to permit a train movement in the opposite direction if desired.

It is now assumed that a westbound train approaches through the main track of station Z. It is obvious from Fig. 2 that signal 6G is in its stop position and has been for some time as the train approached, specifically, since the train passes westbound distant signal 1G in approach to station Z. Further, with relay 6DP released, the reverse code in section 5-7T is of negative polarity, which results in the master code. in section 7-8T being of the 120 code rate. Signal 8Gthus displays an approach indication, which is confirmed by the diagram of Fig. 2. As this train passes signal 5G displaying a green aspect and shunts the rails of section 5-7T, relay 5TR is deenergized and ceases to follow the code pulses from the west. This is followed by the deenergization of relays STP and SRC in order. Likewise, relays SDTFP and 5CD release since they are deenergized due to the nonoperation of the code following contacts of relays STR and STP. Their release is followed shortly by release of relay 5H, deenergized by the opening of front contacts a of the other decoding relays. The red lamp of signal 5G is now energized over back contact b of relay 5H. The release of relay 5CD to open its front contact b interrupts the energizing circuit for relay 6RC so that it cannot subsequently follow the code operation of relay 6TP. The

opening of front contact a of relay 5H deenergizes relay SHP which releases to pole-change the connections from battery 6TB to the track circuit.

At the location of signal 7G, relay A8TR is deenergized by the shunt on the track section and ceases to follow code, all its contacts remaining released with back contacts closed. Relays A8HTFP and A8H release shortly in order, relay A8DTFP having previously released when the reverse code was pole-changed. This transfers the control of relay 7CTP to code transmitter 75CT, the selection being made over back contact a of relay ASH, the circuits further including contacts a of transmitter 750T and back contacts an and ar of relay ASTR. At this time, there is no change in the control circuits for relay ASCTP and this relay continuesto operate at the 180 code rate.

With relay 7CTP operating at the 75 code rate, relay 8TR at signal location 8G is energized by the transmitted code pulses and now follows the 75 code rate. Contact c of relay STP ceases to operate, since it is tuned to the opening of front contact of relay 8H}. Signal 8G is operated to its stop position, the red lamp being energized over an obvious circuit including back contact b of relay 8H. Relay STP follows the coding action of relay 8TR and its front contact repeater relay 8TFP remains energized. Relay SRC likewise follows the coding operation and continues to transmit a reverse code of positive polarity, the code rate being immaterial to the operation of the system. Signal 7G continues to display a clear indication since there is no change in the reverse code polarity being received by relay 7TR.

Transmitter repeater relay A7CT P is now controlled at the 75 code rate, the circuit including back contact a of relay 8 H, back contact b of relay 8S, contacts-a of transmitter 75CT, and at times back contacts an and ar of relay A7TR. The master code transmitted westward through section 8-10T thus changes to the 75 code rate. Since the section is unoccupied atpresent, relay 10TR is energized by these pulses and operates at the same code rate, its contacts controlling the operation of relay 10TP at the 75 code rate also. Relay 10TFP remains energized since it repeats the operation of relay 10TP at any code rate. However, relays ltlDTFP and 10H release at this time since the decoding circuit arrangement for the master code at this location is responsive only to the 180 and 120 code rates, contacts 0 of relays 10TR and 10TP being tuned, respectively, to these higher code rates. Signal 10G changes from the clear to the stop indication, the red lamp being lighted by an obvious circuit over back contact b of relay 10H. Relay 10HP is also deenergized by the opening of front contact c of relay 10H and releases at the termination of its slow re as p r qdh 294 1 5 a n. m slay .Q Q....

controlled by front contact a of relayitl'll since the remainder of the energizing circuit remainspintact at this time. Reverse code of positive polarity continues to be transmitted eastward through sectionB-lfll and maintainsthe existing condition of the code repeating apparatus at the location of signal 8G. There is thus no change in the reversecode tnansmitted eastward to the location of signal 7G and this latter signal remains in its clear position. I

With relays 10H and 10S released, code transmitter repeater relay 9CTP is controlled by transmitter 756T.

This control is established over back contact a of relay 10H and back contact b 'of relay 108. The master code transmitted westward through section 9-12T is thus at the 75 code rate and track relay I ZTR operates at this rate followed directly by relays 12TP and 12RC. The decoding circuit arrangement at signal 12G is only partially responsive to operation at this 75 code rate, contacts c of relays HTR and 12TP, as is obvious, being responsive individually "only to selected higher code rates. Relay IZDTFP releases followed by relay 12H, relay .lZ CD remaining energized as controlled over contact ,b of relay "12TH Signal 12G thus shifts'to its stop i position, the red lamp being energized over back contact b of relay 12H. v I I The reverse codetransmitted by the operation of front contact b of relay 12RC continues to be of the positive polarity and the normal armature of relay 9TR at signal 9G follows the code. Since the rate of this code is immaterial, there is no change in the indication displayedgby-a signal 9G. Thus, shortly after this westbound train has passed signal 5G, the time being determined by that necessary for the cascaded action just described, signals 12G, 10G, and 8G are controlled to their stop position displaying a red aspect. All master code throughout the stretch with the exception of that being transmitted eastward by relay ASCTP at signal 7G is at the code rate. It is to be remembered, of

course, that the master code transmitted eastward from.

contact b of relay I-ZCD, back contact a of relayalZl-I, front and back contacts a of transmitter CT, .andat times back contacts an and ar of relay 11TR. }If.wc now assume thatFi'g. 1B is placed to the left of Fig. .IA, so that the main track section through station X is complete, relay 6TR now follows the 120 code rate'and-relay 6T P directly repeats this code operation. Relay 6DTFP releases and 6HTFP isenergized sincecontact c of relayv 6TP, which is operating at the 120 codegrate, is responsive to alternately close its front and back contacts. Relay 6H holds energized Thus, signaL6G 'is controlled to its approach positiornthe yellow lamp being energized over front contact b of relay 6H and back contact b of relay 6DTFP. This action, referring to Fig. 2, occurs, of course, at'the west. end of station X so that signal 14G shifts to its approach position. Referring again to Fig. 1E, relay 6DP is deenergized at this time by the opening of front contact 0 of relay 6D'IFP so that the former relayreleases and pole-changes the reverse code being transmitted westward into section '5-7T which represents the track section to the west 'of station X in this description. Thus, the reverse armature of the track relay at the far end of the tracksection follows the coded action and the HTFP relay picks: up, the DTFP relay releasing and the H relay holding. Using Fig. ID as a specific example, transmitting relay 7CTP would be shifted to the 120 code rate so that signal 86 would obviously shift to its approach position. In other .w r 9u sh w as epresentatives mt At this time, relay 11CTP (Fig. 1A) is shifted in. operation to the 120 code'rate, the control circuit in- 'cluding normal and reverse contacts b. of the relay, front the reverse code. in the condition of the decoding relay arrangement and those west of station X, it'i's obvious that are distance signal to the rear of signal 146, referring to Fig. 2, also occupiesthe approach positionso that with signal 126 at the stop indication, the two signals to the rear which control the movement, of an eastbound train display an approach indication. Although the code transmitted west into the next two and signal 56 would remain in its clear position. The

reverse code transmitted by relay 6RC, repeating the operation of relay 6TP, remains of the positive polarity so that the normal armature of track relay 11TR follows There is thus no change at this time signal 11G remains in its clear position, the green lamp being lighted as indicated.

Returning to station Z, when the westbound train clears section 3 6T, relay 61 R resumes its code following operation. If assumed, for purposes of this description, that thereis no following train, the code pulses are at the 180 code rate. Relays GDTFP and 6H are thus energized by the decoding arrangement, as previously described, and signal 66 is controlled to its clear position, the green lamp being energized as shown. However, relay 6RC remains deenergized since its circuit is open at front contact b of relay CD, which is deenergiz'ed with the train occupying section 5-7T. Thus, no

reverse code is transmitted eastward through the main track section at station Z and the track relay at the eastern end of this section remains inoperative and signal 36 (Fig.2) remains at the stop position.

As the train approaches signal 76, series approach relay 7A is eventually sufliciently energized to follow the code pulses. Relay 7AP is periodically energized and picks up to hold its front contacts closed in a manner previously described. As the train passes signal 7G,

which is displaying a clear indication, series approach relay 7AA immediately follows the code pulses being circuit is complete for energizing directional stick relay 7S. Tbis circuit is traced from terminal B over front contacta of relay 7AP,"front contact a of relay 7AAP, from contact a of relay 7H, and the winding of relay 7S to'terminal N. The closing of front contact a of relay 7S completes an initial stick circuit for this relay. The

final stick circuit is completed by the closing of back contact a of relay 7H when it eventually releases and relay 75 is thus held energized as long as home relay 7H remains released.

At the west end of section 7-8T, the shunt of the rails by the train deenergizes relay 8TR and it remains with its back contacts closed. Relays 8TP and SRC are likewise de'energized by the halting of the code following action of the track relay. Front contact repeater relay STFP is deenergized when contact b of relay STP remains released and relay 8TFP shortly releases. Since relays SDTFP, SHTFP, 8H, and 8HP are already released due to the master code being at the 75 code rate,

there is no further change in the decoding arrangement at this location.

At this time, the control circuit for relay A8CTP at signal 7G is shifted to the 120 code transmitter. This l "selection is made over back contact 0 of relay 7H and front -contact b of stickrelay 78, the remainder of the circuit including front and back contacts b of transmitter 120CT and at times back contacts an and ar of relay A8TR. When the train clears section 5-7T, master code at the 120 rate is transmitted eastward through the section so that relays STR, STP, and SRC operate at this code rate. Contact c of relay 5TP is responsive to the 120 code rate to alternately close its front and back contacts so that the decoding circuit arrangement is effective to energize relays 5H and 5CD, which pick up and hold as the decoding action'continues. This completes a circuit for energizing the yellow lamp of signal 56 over front contact 12 of relay 5H and back contact b of relay SDTFP so that the signal displays an approach indication for a following train.

The energizing circuit for relay 6RC is now complete at front contact b of relay SOD and relay 6RC repeats the code following operation of relay 6TP. Reverse code is now transmitted eastward through section 3-6T. Since relay SHP is obviously energized over front contact a of relay 5H, the reverse code is of positive polarity. Using Fig. 1A to represent the east end ofsection 3-6T, it is obvious that the normal armature of relay 11TR will operate to follow this positive reverse code. Relays 11DTFP and 11H are energized and pick up so that signal 11G, which represents signal 3G in Fig. 2, is shifted from its stop to clear position, the green lamp being energized over a previously traced circuit. It is to be noted that this signal thus displays no approach indication at any time for a following move, operating directly from its stop to its clear indication. With relay 11D? now' picked up, referring again to Fig. 1A, since front contacts a and c of relays 11H and llDTFP, respectively, are closed, the reverse code transmitted eastward from this location changes to the positive polarity so that the distance signal for westbound moves, signal 16 in Fig. 2, is controlled to its clear indication from the approach indication, that is, from the yellow aspect to the green aspect.

Returning now to Fig. 1B, the location of signal 56, which is now receiving master code from the west at the 120 code rate, as previously described, relay SRC operates to transmit the reverse code westward though the section, the polarity being positive since relay 6DP is energized and picked up. The normal armature of relay ASTR thus follows this reverse code so that the decoding arrangement operates to energize relay ASDTFP. since relay 7AP is now released and its back contact b closed. However, relay A8H remains deenergized since its energizing circuit is interrupted at back contact 0 of relay 78, which is held energized by its stick Cll'Cllll'.. Thus relay 7CTP remains controlled by transmitter CT over back contact a of relay A8H and there is no change in the master code being transmitted into the rails of section 7-8T which are presently shunted by wheels and axles of the westbound train.

As this westbound train passes the location of signal 86, it shunts the rails of section 840T. Relay A7TR ceases its code following operation and remains with its back contacts closed. Since master code continues to be transmitted into the rails, relay 8A immediately follows this code and its repeater relay 8AP picks up and holds. With relay A7TR inoperative and back contact b of relay 8AP open, the decoding circuit arrangement is deenergized at this location and relays A7DTFP and A7H release. Under these conditions, however, relay is not energized, even though front contact a of relay SAP and back contact b of relay STFP are closed, since relay 8HP is released and its front contact (I thus open, interrupting the energizing circuit for relay 85 as is proper for a westbound train. Thus, at this time. there is no change in the control circuit for relay A7CT P and this relay continues to follow the 75 code rate as 

